package queue;

public class LoopQueue<E> implements Queue<E> {
    private E[] data;
    private int front;
    private int tail;
    private int size;

    public LoopQueue(int capacity) {
        // 浪费一个空间来满足循环队列满的条件
        data = (E[])new Object[capacity + 1];
        front = 0;
        tail = 0;
        size = 0;
    }

    public LoopQueue() {
        this(10);
    }

    @Override
    public void enqueue(E e) {
        if((tail + 1) % data.length == front){
            resize(getCapacity() * 2);
        }
        data[tail] = e;
        tail = (tail + 1) % data.length;
        size++;
    }

    @Override
    public E dequeue() {
        if(isEmpty()){
            throw new IllegalArgumentException("cannot dequeue form empty queue");
        }
        E ret = data[front];
        data[front] = null;
        front = (front + 1) % data.length;
        size--;
        if(size == getCapacity() / 4 && getCapacity()/2 != 0){
            resize(getCapacity()/2);
        }
        return ret;
    }

    @Override
    public E getFront() {
        if(isEmpty()){
            throw new IllegalArgumentException("cannot dequeue form empty queue");
        }
        return data[front];
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        // front == queue 空
        return front == tail;
    }

    public int getCapacity(){
        // 浪费一个满足循环队列满的条件
        return data.length - 1;
    }

    private void resize(int capacity){
        E[] newData = (E[]) new Object[capacity + 1];
        for (int i = 0; i < size; i++) {
            // 循环队列，有 offset
            newData[i] = data[(i + front) % data.length];
        }
        data = newData;
        front = 0;
        tail = size;
    }

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append(String.format("queue size=%d, capacity=%d\n",size,getCapacity()));
        res.append("front [");
        for (int i = front; i != tail ; i = (i + 1) % data.length) {
            res.append(data[i]);
            if((i + 1) % data.length != tail){
                res.append(", ");
            }
        }
        res.append("] tail");
        return res.toString();
    }
}
